The current project investigates the effects of prenatal exposure to polychlorinated biphenyls (PCBs) n cognitive development in school-age children. The Oswego Newborn and Infant Development Project tracks the development of 224 children born to women who did or did not consume Great Lakes fish during pregnancy. An established database of umbilical cord levels of PCBs, DDE, Mirex, HCB, lead, EP and hair mercury are on file for every child in the project. In addition, an extensive database of demographic, substance use, and labor/delivery variables containing well over 100 potentially confounding or mediating variables is interleaved with the cord blood database. These data, combined with extremely low project attrition over the past 6 years, provides the opportunity to assess the impact of PCBs and related contaminants on cognitive development. Recent data from the Oswego Newborn and Infant Development Project indicates that prenatal exposure to PCBs impairs cognitive functioning in children as early as 1 and 3 years of age. The project will now track their progress into the early school-age years. This will be accomplished through the use of domain-specific and global cognitive assessment batteries including the Sternberg test of cognitive processing efficiency, The Wechsler Intelligence Scale for Children (WISC III), and the Woodcock-Johnson Psychoeducational Battery. In addition, behavioral functions shown to be repeatedly affected by PCBs and lead in animal models, specifically fixed-interval performance, will be assessed in the children. All outcome measures will be related to the cord blood database of PCBs, lead, DDE, HCB, Mirex, and mercury levels. Further, analysis of tissue-banked Placenta indicate that the PCB concentration exceeds cord-blood levels by 3-4 orders of magnitude. Analysis of the placenta will dramatically enhance exposure assessment through the virtual absence of any placenta PCB data below the detection limit. Control of over 100 potentially confounding variables will be assessed in a multivariate model. The current project will provide critically needed answers to questions surrounding the putative effects of low level PCB exposure on cognitive and behavioral development, and whether the effects of PCBs and related contaminants on standard psychometric batteries translate into functional deficits in school-related performance.